diff --git a/lib/open4.rb b/lib/open4.rb
index 0bac277..3229860 100644
--- a/lib/open4.rb
+++ b/lib/open4.rb
@@ -179,9 +179,9 @@ def run
 
       begin
         @argv.each do |a, b|
-          @threads << Thread.new(*a) do |*a|
+          @threads << Thread.new(*a) do |*th_a|
             begin
-              b[*a]
+              b[*th_a]
             ensure
               killall rescue nil if $!
               @done.push Thread.current
@@ -210,9 +210,9 @@ def to timeout = nil
 
   def new_thread *a, &b
     cur = Thread.current
-    Thread.new(*a) do |*a|
+    Thread.new(*a) do |*th_a|
       begin
-        b[*a]
+        b[*th_a]
       rescue Exception => e
         cur.raise e
       end
@@ -222,11 +222,11 @@ def new_thread *a, &b
 
   def getopts opts = {}
     lambda do |*args|
-      keys, default, ignored = args
+      keys, _, _ = args
       catch(:opt) do
         [keys].flatten.each do |key|
-          [key, key.to_s, key.to_s.intern].each do |key|
-            throw :opt, opts[key] if opts.has_key?(key)
+          [key, key.to_s, key.to_s.intern].each do |th_key|
+            throw :opt, opts[th_key] if opts.has_key?(th_key)
           end
         end
         default
@@ -255,8 +255,8 @@ def relay src, dst = nil, t = nil
         q = Queue.new
         th = nil
 
-        timer_set = lambda do |t|
-          th = new_thread{ to(t){ q.pop } }
+        timer_set = lambda do |tt|
+          th = new_thread{ to(tt){ q.pop } }
         end
 
         timer_cancel = lambda do |t|
@@ -265,9 +265,9 @@ def relay src, dst = nil, t = nil
 
         timer_set[t]
         begin
-          src.each do |buf|
+          src.each do |inner_buf|
             timer_cancel[t]
-            send_dst[buf]
+            send_dst[inner_buf]
             timer_set[t]
           end
         ensure
@@ -338,17 +338,17 @@ def spawn arg, *argv
 
               te = ThreadEnsemble.new c
 
-              te.add_thread(i, stdin) do |i, stdin|
-                relay stdin, i, stdin_timeout
-                i.close rescue nil
+              te.add_thread(i, stdin) do |th_i, th_stdin|
+                relay stdin, th_i, stdin_timeout
+                th_i.close rescue nil
               end
 
-              te.add_thread(o, stdout) do |o, stdout|
-                relay o, stdout, stdout_timeout
+              te.add_thread(o, stdout) do |th_o, th_stdout|
+                relay th_o, th_stdout, stdout_timeout
               end
 
-              te.add_thread(e, stderr) do |o, stderr|
-                relay e, stderr, stderr_timeout
+              te.add_thread(e, stderr) do |th_o, th_stderr|
+                relay th_e, th_stderr, stderr_timeout
               end
 
               te.run
@@ -382,7 +382,7 @@ def background arg, *argv
       else
         argv.push opts
     end
-    thread = Thread.new(arg, argv){|arg, argv| spawn arg, *argv}
+    thread = Thread.new(arg, argv){|th_arg, th_argv| spawn th_arg, *th_argv}
     sc = class << thread; self; end
     sc.module_eval {
       define_method(:pid){ @pid ||= q.pop }